A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a computer-generated test designed to prevent automated contributions to forums, blogs, and other internet registration systems. They usually take the form of a distorted word or words that the user is required to decode and then type out. If the user-provided word matches the image provided by the computer, then the user is allowed to proceed. They usually look something like this:
The problem with traditional CAPTCHAs is that as image-recognition software becomes more and more advanced, CAPTCHAs need to become more and more distorted to defeat them. Eventually in order to weed out the image-recognition software, CAPTCHAs will become unrecognizable to the legitimate humans as well. CAPTCHAs are also susceptible to mechanical turk attacks. That is to say, even if the CAPTCHA is so good that no computer can decode it, there is always a person willing to spend all day solving them by hand for just a few dollars.
Lemur CATTA is a system that aims to circumvent the downfalls of traditional CAPTCHAs, by using a combination of three levels of identification, with varying difficulties of completion.
The first level (Completion), would show the user a few random sentences, one of which can be found in the article in question. If the user has read the article, they should be able to recognize the sentence immediately. The user has a limited amount of time and is only allowed three guesses, so they do not have the opportunity to search for the answer after seeing the question. This method prevents people who have not read the content from commenting on it.
The second level (Comprehension), would require the user to select a sentence that relates to the article, but is not necessarily found in the article. this is similar to the first level, but can not be completed by a machine searching for sentences in the article.
The third level (Affinity) would require the user to choose a sentence that may have nothing to do with the article in question, but is related to the blog or site on which the article is found. This would only allow people who are familiar with the entire site to contribute to it. An example would be a band website requiring the user to listen to a 30-second clip of a song by that band and identify the song title before they can contribute. Since most people are not willing to listen to a band’s entire catalog in order to be able to identify one of them so they can submit a single comment, discussion is limited to existing fans of the band.
The developer of lemur CATTA emphasizes that the system is not a substitute for moderation, but an alternative to traditional CAPTCHAs. There will always be someone with enough determination to defeat any authenticity test. The best defense against unwanted comments is to just delete them.
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